As a part of the development of passive optical pressure and temperature sensors for Aerospace fuel systems applications, an issue was identified that relates to calibration data for the sensors. More particularly, sensors require calibration data to be stored and used to convert the raw measurands into meaningful pressure and temperature values to be used in the fuel gauging system. These calibration data are stored on an optical interrogator, which is remotely located from the sensors themselves. This potentially leads to an issue with interchangeability, as when a sensor is removed and replaced with a different sensor (as may be the case say in a routine line maintenance operation), the calibration data associated with the new sensor must be uploaded onto the interrogator.
In the context of an aircraft fuel gauging system, such an operation is not acceptable to the end customer, as it represents a significant maintenance overhead and a potential cause of system mis-operation if the incorrect data is loaded. It is preferable that any sensor be “plug and play”—that is, once a new sensor is plugged into the interrogator, its data is automatically properly calibrated.
Such an approach is typically taken with high accuracy electrical sensors, where sensor calibration data can be stored locally on the sensor itself, and applied to the raw measurands directly by the sensor in some local processing capability, so that the data output on the electrical data link is immediately usable to the end system. Such systems, however, rely on electrical power provided by a power source to store and retrieve data.
In a fuel tank application, the amount of electrical power must be kept below prescribed levels to prevent the electrical power from acting as a source (electrical spark) that may ignite the fuel/fuel vapor. Such low power levels are generally insufficient to operate the storage devices that store the calibration data. Therefore, such conventional systems are unsatisfactory in an aircraft fuel tank environment.
Therefore, there is a need for an equivalent system for passive optical sensors which allows their interfacing electronics (the interrogator) to automatically read any associated calibration data upon start up, and automatically apply said calibration data to the raw measurands, without the need for any additional manual step during installation.